Yogurt is a combination of dairy ingredients such as whole milk, partially skimmed milk, skim milk, nonfat dry milk, and the like which has been cultured to a specific acidity at high temperatures with an appropriate bacterial culture consisting of Lactobacillus bulgaricus, a rod-shaped lactic acid forming bacterium, and Streptococcus thermophilus, a coccus-shaped bacterium. Production begins with the homogenization and pasteurization of the dairy ingredients at high temperatures followed by cooling to 40.degree. C.-50.degree. C. for inoculation with the culture. The culture is allowed to grow and produce acid to a pH at which curdling or coagulation will occur. Acid production is slowed by cooling the mixture to a temperature between 0.degree. C. and 5.degree. C. The yogurt can be customized to the consumers' taste through the use of sweeteners, fruit, colorants, flavorants, and stabilizers.
Yogurts can be produced in a variety of consistencies such as firm or "gel-like", frozen, or liquid yogurts. Most yogurt presently produced in the United States is of the firm or gelled variety having a spoonable, pudding-like consistency. After a few days of standing the firm yogurt may show signs of syneresis in which a watery substance is seen on top of and around the yogurt. This "wheying off" can be eliminated by increasing the milk solids in the yogurt or by using stabilizers.
Stabilizers commercially available include plant exudates (e.g., gum arabic), seaweed extracts (e.g., alginates), plant and seed gums (e.g., guar gum), animal derivatives (e.g., gelatin) and plant extracts (e.g., pectin). These stabilizers are soluble in milk or already prepared yogurt, and may therefore, be incorporated at any stage of manufacture.
Most of the gelled or firm yogurt produced in the United States is cultured after the dairy ingredient mix, stabilizers and sweeteners are packaged into the container in which it is sold. If however, 1-methyl-N-1-alpha-aspartyl-1-phenylalanine (aspartame.RTM., G. D. Searle & Co., Chicago, Ill.), is used as the sweetening agent, problems arise due to the tendency of aspartame to clump and resist hydration when mixed with the ingredient mix prior to the start of the culturing reactions. In food systems such as the dairy ingredient starter mixes having a pH of above about 5.0, the aspartame will also begin to break down to diketopiperazine (DKP) causing a dramatic reduction in sweetness as described by B. K. Dwivedi in Low Calorie and Special Dietary Foods, C.R.C. Press, Inc., West Palm Beach, Fla. (1978) at pages 77-82. Although this by-product has a minimal effect on taste, the loss of aspartame reduces the sweetness detected in the product. Therefore, Dwivedi recommends that aspartame be added to yogurt as a dry mix of flavor and color after the cultering of the milk has been completed and the pH of the product has been sufficiently lowered.
Therefore, in order to obtain a gelled yogurt sweetened with aspartame, culturing must be conducted prior to the sweetening and packaging, and the necessary gelation or "second set" must be obtained after the sweetener and stabilizers have been mixed with the yogurt and the resultant product packaged and cooled.
Therefore, it is an object of the present invention to provide a method for sweetening yogurt with aspartame or similar artificial sweeteners so as to provide a satisfactory firm or gelled yogurt upon cooling.
It is another object of the present invention to provide a method for the production of a gelled, artificially sweetened yogurt which achieves a satisfactory "second set" after packaging and cooling.
It is still another object of the present invention to provide a method for the production of artificially sweetened, gelled yogurt which minimizes the possibility of the chemical or biological contamination to the ingredients during processing.